I've seen this phantom attack thing too. I chased the attacks going south and seems to happen in the same chain of islands every time I've reloaded. Is it possible that the attacks are prompted by the carrier passing the islands on the way to somewhere further away? As in rather than taking a beeline from a-->d it's passing through a, b, c, to get to d? If that the case then there isn't an attack, it's more like the enemy carrier is sighted while in enroute to somewhere else. I don't suppose there's any sort of debug command or 'cheat' that would allow you to see the enemy carrier movement to confirm that, is there?